There are commonly unsolved difficult problems in the ground tests and laboratory hardware-in-the-loop tests of the coupled inertial/global positioning system on-board a vehicle such as aircraft, ship and car.
In the ground test, since the vehicle is stationary, the inertial sensor in the global positioning/inertial navigation system can not produce dynamic electronic signals for it is a self-contained device, and the global positioning system receiver can not output dynamic measurements. In other words, it is unable to test the accuracy and errors of a global positioning/inertial integrated system installed on-board vehicle while it is stationary. If the inertial sensor, the global positioning system receiver, and the global positioning/inertial integrated system are installed on-board a ground vehicle such as a car, the tester can still process a motion test by actually driving the ground vehicle in relatively low cost. However, if the vehicle to be test is an aircraft, the cost and labors for actual-fly test are ultimately expensive.
In order to verify the correctness of the hardware and software elements of a fully coupled positioning system and/or to evaluate system performance on the ground or in the laboratory, the dynamic signals from the global positioning system receiver (GPSR), gyros, and accelerometers are required to excite the fully coupled positioning system. The present invention is related generally to a method for gyro, accelerometer, and global positioning system sensor coupled simulation.
The static test of a fully coupled positioning system is easy where the actual inertial sensors and global positioning system receiver can be used. The fully coupled positioning system is often installed on a moving platform, so that a dynamic test of the fully coupled positioning system is required before a mission. Obviously, the static method cannot be applied to the fully coupled positioning system dynamic test where the dynamic inertial measurements and global positioning system signals are required. Therefore, it is necessary that the essential parts of the gyros, accelerometers, and global positioning system receiver experience a trajectory identical to the expected mission for dynamic testing of the fully coupled positioning system.
The flight test provides a real environment for the fully coupled positioning system. A set of real flight tests is costly, and often not affordable during the development of a fully coupled positioning system. Also, before the flight test, the fully coupled positioning system must go through a series of official tests. Thus, a real time hardware-in-the-loop simulation of a gyro, accelerometer, and a global positioning system receiver is necessary during the development of a fully coupled positioning system as well as for a fully coupled positioning dynamic test before a mission.
A straightforward method for generating dynamic inertial measurements is to put an actual inertial sensor on a motion table. This method requires a large set of testing equipment. Moreover, its operational cost is high. Its dynamic motion is limited. Its data acquisition process during the test is not convenient. It cannot be used for simultaneous generation of dynamic global positioning system receiver measurements.
Some systems for global positioning system signal simulation generate suppressed radio frequency (RF) analog signals to test a global positioning system receiver. The RF output mimics the global positioning system signal emitted from the global positioning system satellites by modulating pseudo random noise code and navigation message data, such as ephemeris, clock parameters, even atmospheric data, on an L-band carrier (1,575.42 MHz) or two L-band carriers (1,575.42 MHz and 1,227.60 MHz). The simulated signal has the same amplitude and signal-to-noise ratio (SNR) as realistic one so that it can be directly injected into a global positioning system receiver through the antenna port.